Chlorine-containing compounds, such as chlorofluorocarbons (CFCs), have been employed as refrigerants, foam blowing agents, cleaning agents, solvents, heat transfer media, sterilants, aerosol propellants, dielectrics, fire extinguishing agents, and power cycle working fluids. However, CFCs have proven to be detrimental to the Earth's ozone layer. Conventional substitutes for CFCs include hydrofluorocarbons (HFCs); however, these compounds have been found to contribute to global warming. For these reasons, there is a worldwide effort to develop new compounds that are environmentally benign.
Partly or fully fluorinated olefins, including hydrofluoroolefins, (collectively referred to hereinafter as fluorinated olefins) are potential replacements for HFCs and CFCs. They can be used in some of the aforementioned applications and can also be used as feedstock monomers to synthesize fluoropolymers and other macromolecular compounds.
Various methods for producing certain fluorinated olefins are known, including those involving the dehydrochlorination of hydrochlorofluorocarbons. For example, U.S. patent application Ser. No. 11/619,592 discloses a method for preparing 2,3,3,3-tetrafluoropropene (1234yf) via dehydrochlorination of 2-chloro-1,1,1,2-tetrafluoropropane (244bb) with the aid of a catalyst. The 244bb reactant can be prepared through liquid phase or gas phase catalytic fluorination of 1,1,1-trifluoro-2-chloropropene (1233xf) with HF and 1233xf, in turn, can be made via gas phase fluorination of CCl2═CCl—CH2Cl (1,1,2,3-tetrachloropropene) with HF. The '592 application also teaches the use of a carbon- and/or metal-based catalyst for the conversion of 244bb to 1234yf. Depending on the reaction conditions, the conversion of 244bb could be as high as 98%, but it has selectivity for 1234yf of only 69% to 86%. Thus, there remains a need to develop a commercially viable catalyst that not only is active, but also is more selective for 1234yf.
However, the conversion of a hydrochlorofluorocarbon to a fluorinated olefin by conventional methods is problematic because by-products often form and compete in the dehydrofluorination reaction, thereby reducing the yield of the desired fluorinated olefin. Hence, it would be advantageous to develop a catalyst system that can suppress undesirable dehydrofluorination reactions, so that single-pass productivity and yield of the desired fluorinated olefin can be increased.